Method of forming surface alloys on metallic articles



1- alm Oct; 2'7, 1959 P. VULLIEZ METHOD OF FORMING SURFACE ALLOYS ON METALLIC ARTICLES Filed June 15, 1956 2 Sheets-Sheet 1 PHUA I uLL EZ P. VULLIEZ METHOD OF FORMING SURFACE ALLOYS ON METALLIC ARTICLES Filed June 15, 1956 2 Sheets-Sheet 2 a w i k x v m. m

United States Patent .METHOD OF FORMJNG SURFACE ALLOYS ON METALLIC ARTICLES Paul Vulliez, Pont-Audemer, France Application June 15, 1956, Serial No. 591,604 Claims priority, application France June 30, 1955 13 Claims. (Cl. 117-94 The present invention relates to a process of formation of a surface alloy by the diffusion in the gaseous phase of an added metal, in which the metallic articles to be treated are heated in a furnace to a suitable temperature in a conditioned atmosphere and in the presence of the said added metal and also in general of an appropriate reagent. I

In the known processes of this kind, the articles to be treated are arranged in the form of pieces in bulk or in the form of powder. These processes may be satisfactory but they sometimes have drawbacks such as defects of uniformity in the added coating, pitting, etc. In addition, these known methods are not suitable for all applications.

The present invention has for its object a process of formation of a surface alloy on metallic members by the ditfusion in the gaseous phase of an added metal, which is not subject to the drawbacks referred to above.

A process in accordance with the invention is characterised in that the added metal consists of one or more members, previously sintered and having adequate porosity. This arrangement results in an excellent uniformity of the added coating and irreproachable finish of the completed articles, whilst the added metal remains substantially without contamination during the course of the operations, and lends itself to an intimate and effective cooperation with the reagent. The latter may be a liquid such as a halogen acid, for example hydrofluoric acid or other like acid, with which the sinteredclements are impregnated; it may be solid, preferably in powdered form, such as an appropriate halide, or it may be incorporated in all or part of the sintered elements, preferably in housings previously formed for that purpose, or arranged alongside the said elements; or again, it may be gaseous such as a halogen, preferably fluorine, in troduced into the midst or in the vicinity of the sintered members.

The sintered members in accordance with the invention may be divided in the form of a large number of particles such as balls; these latter are arranged to surround the articles to be treated, in the same way as the pieces of metal employed up to the present time, but have however a considerably increased effectiveness as compared with previous processes.

In accordance with a further special feature of the invention, the sintered elements are preferably provided of larger size and are so shaped that they are wholly or in part adapted to follow or even to have the same shape as the surface to be treated, whilst being separated therefrom by a smallspace or by no space at all, and the said elements are fitted in the same way as casings or cores on or inside the articles to be treated.

In the case of small articles treated in series production, a single sintered casing may be provided with a more or less considerable number of cells, each of these cells being intended to receive one of the small articles. A number .of sintered cases thus fitted may be stacked one on the other inside a single crucible, and this arrange.

meat gives an appreciable improvement, both as regards space occupied and time of operation.

In a general way, the treatment of the articles which is carried out in a furnace at a suitable temperature and in a suitably-conditioned reducing atmosphere, may be carried out in accordance with the invention in a noncontinuous manner, that is to say the articles are placed in a furnace and they are left there until the end of the operation, after which they are taken out, but preferably, and in an application of the invention which is still more especially, but not exclusively directed to the treatment of long sections such as tubes, thin sheets, etc., a continuous method is employed, that is to say the articles pass into the furnace one after the other, and are treated between the moment at which they are admitted to the furnace and the moment at which they pass out of the said furnace.

With a view to an operation of this kind, the sintered elements in accordance with the invention may accompany the articles as they pass through the furnace, or again they may be mounted so as to be stationary inside the furnace and will thus have a relative movement with respect to the articles. In both these cases, the direction of movement of the articles inside the furnace may be vertical, horizontal or inclined at an angle, and the sintered elements preferably consist of blocks arranged alongside each other and/ or stacked one on top of the other and arranged so as to form by their whole assembly, for example either a tunnel or a chimney in the case of the treatment of an external contour of an article, or of a core in the case of the treatment of an internal contour.

The invention has also for its object an arrangement for carrying into effect the method referred to above, together with the articles treated by this process and/or by the use of the said arrangement.

Forms of embodiment of the invention will now be described below by way of example, reference being made to the accompanying drawings, in which:

Fig. l is a view in vertical cross-section of a crucible provided with sintered multi-cellular casings for the treatment of small articles;

Fig. 2 -is a diagrammatic view in vertical cross-section of a furnace for the continuous treatment of tubes;

Fig. 3 is a view of the same furnace in cross-section taken along the line IIIIII of Pig. 2;

Fig. 4 concerns a modified part of the installation shown in Fig. 2;

Fig. 5 relates to a further alternative form of embodiment.

Reference will first be made to Fig. l which refers by way of example to an application of the invention to the treatment, by coating with chromium, of small mass-produced articles P, such as pinions, screws or the like. With a view to plating these articles with chromium, the articles P are housed in cells A, a large number of which is formed in the casings B, one articles P being placed in each cell A. Each casing E is made up of previously-sintered chromium powder. A number of such casings Bare stacked one above the other in the same crucible R. The cells of each casing are covered-in and closed by the casing immediately above it, whilst a lid C ensures the closure of the cells of the casing on top of the stack. In addition, a halogenated reagent is admitted to the centre or in the vicinity of the casings.

The crucible R is passed into the furnace at a suitable temperature and in a reducing atmosphere. After the required time, the articles P are coated with a layer of chromium which is perfectly uniform and free from pitting or other defects.

Reference will now be made to Figs. 2 and 3, which relate by way. of example to'an application of the invention to the treatment of the exterior of tubes or other members of constant section, by coating with chromium. There will be seen in Fig. 2 a furnace shown at 1, the base-plate of the furnace at 2, at 3 a pre-heating chamber, and at 4 a cooling chamber, at 5 a fixed sheath of refractory steel passing right through the assembly of the pre-heating chamber 3, the furnace 2 and the cooling chamber 4. The extremites of the fixed sheath 5 project slightly to the exterior, and are respectively provided, one with a supply pipe 6 for admitting hydrogen and the other with an evacuation pipe 7.

A series of tube-supports 8, 9, 10, 11, are connected together end to end by means of sleeves 12, 13 and 14, each of which comprises a central flange, the dimensions of which are identical with the external dimensions of the tube-supports, and two symmetrical portions being adapted to engage in one extremity of the support tube, thus serving as a plug. Within the interior of a tube support, there may be disposed elements 15 in one or two parts, of sintered added metal which form a sheath in the interior of which is placed the tube 16 to be treated.

At their point of entry and of exit from the fixed sheath 5, the different tube-supports pass through a seal ing device (not shown) which may be for example a packing gland with a fitting of asbestos.

The rate of forward travel of the tube-supports is adjusted in such manner that each point of a tube remains in the heating section of the furnace for the time required to ensure a normal chromium treatment of the article to be plated.

Fig. 3 shows a cross-section in accordance with the line IIIIII of Fig. 2, of a furnace in accordance with the invention, equipped with five fixed sheaths 5a, 5b, 5c, 5d and 5e, placed on the sole plate 2 of the furnace. Inside these sheets are passed the tube-supports which are provided with elements 15 of sintered added metal. The elements 15 are arranged so as to surround the tubes 16 to be treated.

It should be noted that by virtue of the well-defined shapes of solid bodies obtained by sintering, the added metal lends itself to an exact location of the reagent, and this permits of a judicious distribution of this reagent, on which the success of the treatment may depend in the case of long articles.

As an alternative form (see Fig. 4), the arrangement is similar to that which has just been described with reference to Figs. 2 and 3, except that the tubes are in this case not chromium plated on their outside but on their interior.

In this case, the tubes to be treated play the part of the tube-supports 8 of Fig. 2, and the blocks of sintered chromium 15 are arranged inside the tubes in the same way as cores. The blocks 15 are preferably themselves made hollow in order that at least one of them may be given a suitable charge of reagent as has been shown at 20.

In the forms of embodiment of Figs. 2 and 3 and of Fig. 4, the sintered blocks travel along with the articles to be treated during the travel of these articles inside the furnace. In the alternative form of embodiment which will now be described with reference to Fig. 5, the sintered blocks are stacked in a fixed position inside the furnace and thus have a relative movement with respect to the articles.

In Fig. 5, the furnace is shown at 21, and the muffle at '22, in which the annular elements 23 of sintered added metal are arranged one on top of the other. A joggle 24 enables these elements to be centered with accuracy so that they constitute a perfectly cylindrical central sheath 25, inside which passes the tube 26 to be treated.

'The tube is held in alignment with the sheath 25 by means of guiding devices formed by at least two pairs of pulleys 27 and 28.

The movements of the pulleys 27 and 28 are regulated in order to ensure either a continuous uniform downward Cir movement of the tube 26 or a downward movement in steps with prolonged stoppages. These movements are also conjugated in such manner that the pulleys 27 which carry the weight of the upper portion of the tube 26 and that of the tube which follows, whilst the pulleys 28 carry the lower portion of the tube 26, which has already been treated.

The tube 26 penetrates into the chamber of the furnace through a sealing member 29 located at the top of an entry chamber 30, that is to say in a relatively cold zone. The member 29 preferably consists of packing glands which are adapted to have an inert gas passed through them. In a similar way, the tube 26 passes out of the furnace through a cooling chamber 31, passing through a sealing member 32 if this is necessary. Hydrogen is introduced at 33 at the top of the chamber 40 and passes out of the base of the furnace at 34.

The sintered elements are each pierced with one or a number of holes such as 35, thus forming a vertical conduit shut-off at 36 at the upper portion and through which the reagent may be introduced through the orifice 37, passing through the cooling chamber 31 by a tube 38. Passages 40, which are preferably radial, may be formed in one or a number of sintered blocks 23 and extend between the conduit 35 and the sheath 25 so as to form a communication between these latter.

A junction member 39 provides the continuity between the successive tubes 26. This member is of sintered plating metal when the extreme faces of the tubes are to be treated.

What I claim is:

1. A method of formation of a surface alloy coating by diffusion in the gaseous phase of a coating-metal, in which the metallic articles to be coated are heated in a reducing furnace in the vicinity of the coating-metal and in the presence of a halide, the said coating-metal being constituted by at least one element which has previously been sintered to a porous state.

2. A method as claimed in claim 1, in which the said sintered elements are so shaped that at least a portion of their surface is arranged to have the same contour as that of the surface to be treated, a small interspace being provided between the surfaces of the said sintered elements and the said articles to be treated, the said elements being fitted, in a similar manner to casings, to the exterior of the said articles.

3. A method as claimed in claim 2, in which the dimension of the said interspace is reduced substantially to zero.

4. A method as claimed in claim 1, in which the said sintered elements are so shaped that at least a portion of their surface is arranged to have the same contour as that of the surface to be treated, a small ip terspace being provided between the surfaces of the said sintered elements and the said articles to be treated, the said elements being fitted, in a similar manner to cores, into the interior of the said articles.

5. A method as claimed in claim 4, in which the dimension of the said interspace is reduced substantially to nil.

6. A method as claimed in claim 1, in which the said halide is inserted into housings formed for that purpose in the said sintered elements. 7

7. Articles on which a surface alloy is formed as a coating, produced by the method of treatment as claimed in claim 1.

8. A method of formation of a surface alloy on small mass-produced articles by diffustion in the gaseous phase of a coating-metal comprising the steps of preparing a casing constituted by a shaped member of presintered porous coating-metal and having cells therein, placing the said articles in said cells, placing said casing in a crucible, and placing said crucible in a heating furnace while maintaining a reducing atmosphere therein in the presence of a halide.

9. A method as claimed in claim 8, wherein a plurality of said casings is provided, the said casings being formed and arranged so that they may be stacked one above the other, comprising the step of stacking said casings one above the other in the same crucible.

10. A method of formation of a surface alloy on elongated articles by diffusion in the gaseous phase of a coating-metal, comprising steps of preparing elements of presintered porous coating-metal, placing said elements in the vicinity of said articles and conveying said articles and elements as a whole through a heating furnace while maintaining a reducing atmosphere therein in the presence of a halide.

11. A method as claimed in claim 10, comprising the step of guiding said articles and elements in the direction of the length of said articles.

12. A method of formation of a surface alloy on elongated articles by ditfusion in the gaseous phase of a coating-metal, comprising the steps of preparing elements of presintered porous coating-metal, placing these elements stationary in a heating furnace and conveying said articles through said furnace in the vicinity of said elements while maintaining a reducing atmosphere therein in the presence of a halide.

13. A method as claimed in claim 1.2 wherein said elements are stackable comprising the step of stacking said elements in said furnace.

References Cited in the file of this patent UNITED STATES PATENTS 116,158 Clark June 20, 1871 964,871 Johnson July 19, 1910 1,902,503 Howe Mar. 21, 1933 2,622,043 Roush Dec. 16, 1952 FOREIGN PATENTS 160,812 Australia Jan. 28, 1955 363,954 Great Britain Dec. 31, 1931 533,644 Germany Sept. 3, 1931 686,097 Great Britain Jan. 21, 1953 

1. A METHOD OF FORMATION OF A SURFACE ALLOY COATING BY DIFFUSION IN THE GASEOUS PHASE OF A COATING-METAL, IN WHICH THEMETALLIC ARTICLES TO BE COATED ATE HEATED IN A REDUCING FURNACE IN THE VINCINITY OF THE COATING-METAL AND IN THE PRESENCE OF A HALIDE, THE SAID COATING-METAL BEING CONSTITUTED BY AT LEAST ON ELEMENT WHICH HAS PREVIOUSLY BEEN SINTERED TO A POROUS STATE. 